1. Field of the Invention
The present invention relates to a method and a apparatus for measuring the insulation resistance of an electronic component. Particularly, the invention relates to a method for removing the influences of noise due to mechanical vibrations occurring in equipment for checking the characteristics of an electronic component having the piezoelectric effect.
2. Description of the Related Art
Conventionally, a measuring circuit is used to measure the insulation resistance of an electronic component such as a ceramic capacitor. FIG. 1 shows the conventional measuring circuit using a current voltage conversion system. Reference character Rs denotes an inrush current limit resistance of an electronic component 1 as a tested sample, and reference character Rx denotes the insulation resistance of the electronic component 1. The value of Rs is much smaller than the value of Rx. A ceramic capacitor is usually shown by a parallel equivalent circuit composed of the insulation resistance Rx and a capacitance. In this figure, however, only the insulation resistance Rx is provided to simplify the illustration. Reference numeral 2 denotes an operational amplifier having a feedback resistance Rf. In the circumstances, a current i flowing to the electronic component 1 from the output Vo of the operational amplifier 2 is obtained. Then, with a power supply voltage E and the current i, the insulation resistance Rx of the electronic component 1 can be obtained by the following equations.
i=Vo/Rf
Rx=E/i
In this method, the leakage current i is extremely small and there is susceptibility to the influences of noise, although control is simple and a quickly response can be obtained.
In addition, as shown in FIG. 2, there is an insulation resistance measuring circuit using an electric charge accumulating system. One example is described in Japanese Unexamined Utility Model Publication No. 5-064782. In this measuring circuit, a switch SW and a feedback capacitance Cf are connected in parallel between the inverting input terminal of an operational amplifier 2 as a high input impedance amplifier and the output terminal thereof. The switch SW is turned from ON to OFF to measure an output Vo after t seconds. The value of t is, for example, set to be a desired value of approximately 0.1 to 10 seconds. Then, a current i flowing through an electronic component 1 from the output Vo is obtained-by the following equations. In addition, with a power supply voltage E and the current i, the insulation resistance Rx of the electronic component 1 is obtained.
i=Cfxc2x7Vo/t
Rx=E/i
Since the electric charge accumulating circuit serves as an integrator, the circuit can reduce the influences of hums due to a commercial power supply and the like.
When stress is applied to a dielectric member in a situation in which a DC voltage is applied, the piezoelectric effect permits an electric charge according to the stress to be generated from the dielectric member. In general, in apparatuses for checking the characteristics of electronic components, there are used many devices such as a part feeder, a motor, and a hopper, which produce mechanical vibrations due to driving. With the propagation of the vibrations through an electronic component, a noise current due to the piezoelectric effect is generated. However, as mentioned above, a leakage current i, which is measured to obtain the insulation resistance of the electronic component 1, is extremely small. In addition, a piezoelectric noise current occurring due to mechanical vibrations applied to the electronic component 1 is superimposed on the measured current i to make a measurement error.
As a result, the former measuring circuit using the current voltage transformation system cannot remove the influences of noise. In addition, the latter measuring circuit using the electric charge accumulating system cannot remove the influence of the above-mentioned piezoelectric noise current, either.
Accordingly, it is an object of the present invention to provide an insulation resistance measuring method, which can remove the influences of piezoelectric noise due to mechanical vibrations applied to an electronic component and can measure the insulation resistance of the electronic component with high accuracy.
In order to accomplish the above object, according to a first aspect of the present invention, there is provided an insulation resistance measuring method including the steps of applying a predetermined measurement voltage to an electronic component arranged in a position subjected to periodic mechanical vibrations from the outside, measuring a current flowing through the electronic component, and integrating the value of the measured current flowing through the electronic component over the period of the mechanical vibrations or over a time which is an integral multiple of the period thereof to obtain the insulation resistance of the electronic component.
According to a second aspect of the present invention, there is provided an insulation resistance measuring method including the steps of applying a predetermined measured voltage to an electronic component arranged in a position subjected to periodic mechanical vibrations from the outside, measuring a current flowing through the electronic component, and integrating the value of the measured current flowing through the electronic component over a time which is the least common multiple of the period of the mechanical vibrations and the period of a commercial power supply to obtain the insulation resistance of the electronic component.
According to a third aspect of the invention, there is provided an insulation resistance measuring method including the steps of applying a predetermined measured voltage to an electronic component arranged in a position subjected to periodic mechanical vibrations from the outside, measuring a current flowing through the electronic component, in which the period of the mechanical vibrations is equal to or less than xc2xd of the period of a commercial power supply, integrating the value of the measured current flowing through the electronic component over the period of the mechanical vibrations, integrating the value of the measured current flowing through the electronic component over the period of the mechanical vibrations after a time which is xc2xd of the period of the commercial power supply has passed from the onset of the above integration, and obtaining the average of the results from the two integrations.
According to a fourth aspect of the present invention, there is provided an insulation resistance measuring method including the steps of applying a predetermined measurement voltage to an electronic component arranged in a position subjected to periodic mechanical vibrations from the outside, measuring a current flowing through the electronic component, in which the period of a commercial power supply is equal to or less than xc2xd of the period of the mechanical vibrations, integrating the value of the measured current flowing through the electronic component over the period of the commercial power supply, integrating the value of the measured current flowing through the electronic component over the period of the commercial power supply after a time which is xc2xd of the period of the mechanical vibrations has passed from the onset of the integration, and obtaining the average of the results from the two integrations.
According to a fifth aspect of the present invention, there is provided an insulation resistance measuring apparatus including a DC measurement power supply, an electronic component arranged in a position subjected to periodic mechanical vibrations from the outside, and an electric charge accumulating circuit for integrating an input current i to obtain a voltage output Vo so as to obtain the insulation resistance of the electronic component. The DC measurement power supply, the electronic component, and the electric charge accumulating circuit are connected in series to each other. In this apparatus, the integration time of the input current i is set to be the period of the mechanical vibrations or a time which is an integral multiple thereof.
According to a sixth aspect of the present invention, there is provided an insulation resistance measuring apparatus including a DC measurement power supply, an electronic component arranged in a position subjected to periodic mechanical vibrations from the outside, and an electric charge accumulating circuit for integrating an input current i to obtain a voltage output Vo so as to obtain the insulation resistance of the electronic component. The DC measurement power supply, the electronic component, and the electric charge accumulating circuit are connected in series to each other. In this apparatus, the integration time of the input current i is set to be a time which is the least common multiple of the period of the mechanical vibrations and the period of a commercial power supply.
In the insulation resistance measuring method according to the invention, the measurement voltage is applied to the electronic component to measure the current. When the vibrations due to a drive mechanism and the like propagate through the electronic component, a piezoelectric noise current is generated. The piezoelectric noise current has a periodicity in accordance with the vibration frequency of the drive mechanism. A current obtained by superimposing a leakage current to be primarily measured on the piezoelectric noise current is measured. The vibration frequency of the drive mechanism is in advance measured and the value of a measured current flowing through the electronic component is integrated over the period of the mechanical vibrations. With this arrangement, since the piezoelectric noise current is cancelled, only the leakage current to be primarily measured can be extracted. With a calculation based on the current value, the insulation resistance of the electronic component can be detected with high accuracy.
In terms of the integration time, even when integration is performed not only over the period of the mechanical vibrations but also over a time which is the integral multiple thereof, the same result can be obtained.
This method can be used if only the piezoelectric noise has the periodicity, even though the noise has a distorted waveform.
When the noise applied to the electronic component comes from only the vibrations due to a single drive mechanism, the signal of the piezoelectric noise can be effectively removed by integrating over the period of the mechanical vibrations. Meanwhile, when noises caused by the vibrations due to a plurality of drive mechanisms are combined, by integrating over a time which is the least common multiple of the vibration periods of the drive mechanisms, the plurality of piezoelectric noise currents can be simultaneously removed. As a result, only a leakage current to be primarily measured can be extracted. For example, when the vibration frequency of a first drive mechanism is 120 Hz and the vibration frequency of a second drive mechanism is 240 Hz, by integrating over the period of the least common multiple ({fraction (1/120)}=8.3 msec), the two piezoelectric noise currents can be simultaneously removed.
When the noises applied to the electronic component are produced by the combination of the mechanical vibrations due to the drive mechanism and hums due to a commercial power supply, as described above, the combined noise current can be integrated over the period of the least common multiple of the period of the mechanical vibrations and the period of the commercial power supply. For example, when the frequency of the commercial power supply is 60 Hz and the vibration frequency of the drive mechanism is 120 Hz, a measurement apparatus detects, in addition to a leakage current to be primarily measured, a superimposed form of the hum current from the commercial power supply and the piezoelectric noise currents from the drive mechanism. When the current formed by superimposing is integrated over the commercial power-supply period ({fraction (1/60)}=16.7 msec), which is the period of the least common multiple, the hum current and the piezoelectric noise current can be simultaneously removed. Thus, only the leakage current to be primarily measured can be extracted.
This method can be used if only each of the piezoelectric noise and the hum has a periodicity, even though the noises have distorted waveforms.
As described above, preferably, the drive mechanism is designed in advance in such a manner that the frequency of the mechanical vibrations is set to be an integral multiple of the frequency of the commercial power supply or the reciprocal of the integral multiple thereof. With this arrangement, the longest one of the periods of the mechanical vibrations and the period of the commercial power supply is used for integration. Thus, the integration time is not increased.
As described above, both noises can be simultaneously removed by integrating over the period of the least common multiple of the period of the mechanical vibrations and the period of the commercial power supply. However, there is a problem in that the integration time is increased. Thus, when the period of the mechanical vibrations is equal to or less than xc2xd of the period of the commercial power supply, the noises can be removed by the method according to the third aspect of the invention. As a result, the integration time can be shortened. In other words, first, the measured current value is integrated over the period of the mechanical vibrations. Then, after a time which is xc2xd of the period of the commercial power supply has passed from the onset of integration, the measured current value is again integrated over the period of the mechanical vibrations. Thus, only a leakage current to be primarily measured can be extracted by the average of the results from the two integrations.
This method can be applied when the frequency of the mechanical vibrations is higher than the frequency of the commercial power supply. In addition, there is an advantage when hums have normal sine waves, which are not distorted.
In contrast with the above case, when the period of the commercial power supply is equal to or less than xc2xd of the period of the mechanical vibrations, noises can be removed by the method according to the fourth aspect of the invention. As a result, the integration time can be shortened. In other words, first, the measured current value is integrated over the period of the commercial power supply. Then, after a time which is xc2xd of the period of the mechanical vibrations has passed from the onset of integration, the measured current value is again integrated over the period of the commercial power supply. After this, only a leakage current to be primarily measured can be extracted by the average of the results from the two integrations.
This method can be applied when the frequency of the commercial power supply is higher than the frequency of the mechanical vibrations. In addition, there is an advantage when hums have normal sine waves, which are not distorted.
In the measuring apparatus according to the fifth aspect of the invention, the above method of the first aspect of the invention is applied to the circuit using the electric charge accumulating system. In the measuring apparatus according to the sixth aspect of the invention, the method of the""second aspect of the invention is applied to the circuit using the electric charge accumulating system.